In EP-A-0,271,144 a process is disclosed for the carbonylation of acetylenically unsaturated compounds in the presence of a catalyst system that can be formed from a palladium compound, a protic acid, and an organic monophosphine, e.g., diphenyl-2-pyridylphosphine.
A problem encountered with the processes for the carbonylation of acetylenically unsaturated compounds comprises poisoning of the catalyst by the isomeric 1,2-alkadiene compounds (so-called allenes) typically found therein. Small quantities of allenes, for example up to 0.4%, can often be tolerated, but the amounts commonly found in the acetylenic feed stocks present problems that need to be addressed before they can be used for the carbonylation process.
In EP-A-0,441,446 an improved carbonylation catalyst system is suggested that exhibits tolerance (e.g., up to 7%) under basic conditions, i.e., provided a tertiary amine is present (see comparative example G versus example 12). However, there is no suggestion in this reference that further improvements in respect of the carbonylation process, even carried out in the absence of the tertiary amine, could be achieved.
A further improvement in allene tolerance is disclosed in WO 95/05357. According to this document, the process should be conducted in the presence of a catalyst system based on a (di)phosphine having an aromatic substituent which contains an imino nitrogen atom and that is substituted with an electron-withdrawing group in a specified manner.